Dysphagia is a disorder of the swallowing mechanism often leading to aspiration, and is a major problem for stroke and head injury patients. The current clinical methods of evaluation are qualitative and are based on bedside clinical evaluation and videofluorography. Recently, we have identified and developed techniques to noninvasively measure several biomechanical parameters (tongue thrust, throat acceleration etc.) that characterize the swallowing mechanism, and have studied a limited number of patients. The question remains whether these biomechanical measurements are reliable. Another question arises whether the biomechanical (BM) technique is useful to identify the patient at risk of aspiration and to demonstrate the clinical improvements in the patient's swallowing mechanism. In order to answer these questions, BM measurements of the oral and pharyngeal phases will be obtained from three groups of subjects. The first group consisting of normal subjects will be used to study the test-retest reliability. The second group will consist of stroke patients with dysphagia, and the third group will consist of head injury patients with dysphagia. Measurements will be obtained from the dysphagic patients (second and third group) within three days of videofluorographic examination (VFE) upon admission to the hospital and after a three week period, and will be compared with the VFE findings. The results will test our hypothesis that noninvasive biomechanical technique is reliable and can aid the clinician to demonstrate clinical improvements and to identify patients at risk of aspiration.